Turbofan engine

ABSTRACT

A turbofan engine is provided that includes a fan nacelle surrounding a core nacelle. The core nacelle houses a spool. The fan and core nacelles provide a bypass flow path having a nozzle exit area. A turbofan is arranged within the fan nacelle upstream from the core nacelle. A flow control device is adapted to effectively change the nozzle exit area to obtain a desired operating condition for the turbofan engine. A gear train couples the spool and turbofan for reducing a turbofan rotational speed relative to a spool rotational speed. A controller is programmed to respond to at least one sensor. The controller is programmed to effectively control the nozzle area.

BACKGROUND OF THE INVENTION

This invention relates to a turbofan engine, and more particularly, theinvention relates to a turbofan engine having an effectively variablenozzle exit area.

A turbofan engine typically includes a fan nacelle surrounding a corenacelle. A spool is housed in the core nacelle and supports a compressorand turbine. A turbofan is arranged in the fan nacelle upstream from thecore nacelle. Flow from the turbofan bypasses the core nacelle through abypass flow path arranged between the core and fan nacelles. The bypassflow path includes an exit nozzle that is typically fixed. In manyturbofan engines, the turbofan is driven directly by the spool androtates at the same speed as the spool.

The engine's design is affected by such factors as the pressure ratio ofthe turbofan. Propulsive efficiency improvements, and hence fuelconsumption, can be gained by reducing the turbofan pressure ratio.Direct drive turbofan engines have several design challenges. In oneexample, the speed of the spool is determined by the appropriate tipspeed for a desired turbofan pressure ratio. In some applications, asthe turbofan pressure ratio is reduced, additional compressor andturbine stages must be added to the spool to obtain the needed amount ofwork from the compressor and turbine at this speed. The result isincreased engine weight and cost.

Some turbofan engines employ structure at the aft portion of the bypassflow path that is used to change the physical area of the nozzle. Thisarrangement enables manipulation of various engine operating conditionsby increasing and decreasing the nozzle area. However, this type ofengine arrangement has used a turbofan driven directly by the spool.

What is needed is a turbofan engine having a turbofan that is decoupledfrom the low spool and provisioned with an effectively adjustable fannozzle that provides improved efficiency.

SUMMARY OF THE INVENTION

A turbofan engine is provided that includes a fan nacelle surrounding acore nacelle. The core nacelle houses a spool. The fan and core nacellesprovide a bypass flow path having a nozzle exit area. A turbofan isarranged within the fan nacelle upstream from the core nacelle. A flowcontrol device is adapted to effectively change the nozzle exit area toobtain a desired operating condition for the turbofan engine. A geartrain couples the spool and turbofan for reducing a turbofan rotationalspeed relative to the spool rotational speed.

These and other features of the present invention can be best understoodfrom the following specification and drawings, where the following is abrief description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an example turbofan engine.

FIG. 2 is a partially broken perspective view of the turbofan engineshown in FIG. 1.

FIG. 3 is a schematic of a gear train shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A geared turbofan engine 10 is shown in FIG. 1. A pylon 38 secures theengine 10 to an aircraft. The engine 10 includes a core nacelle 12 thathouses a low spool 14 and high spool 24 rotatable about an axis A. Thelow spool 14 supports a low pressure compressor 16 and low pressureturbine 18. In the example, the low spool 14 drives a turbofan 20through a gear train 22. The high spool 24 supports a high pressurecompressor 26 and high pressure turbine 28. A combustor 30 is arrangedbetween the high pressure compressor 26 and high pressure turbine 28.Compressed air from compressors 16, 26 mixes with fuel from thecombustor 30 and is expanded in turbines 18, 28.

Airflow enters a fan nacelle 34, which surrounds the core nacelle 12 andturbofan 20. The turbofan 20 directs air into the core nacelle 12, whichis used to drive the turbines 18, 28, as is known in the art. Turbineexhaust E exits the core nacelle 12 once it has been expanded in theturbines 18, 28, in a passage provided between the core nacelle and atail cone 32.

The core nacelle 12 is supported within the fan nacelle 34 by structure36, which are commonly referred to as upper and lower bifurcations. Agenerally annular bypass flow path 39 is arranged between the core andfan nacelles 12, 34. The example illustrated in FIG. 1 depicts a highbypass flow arrangement in which approximately eighty percent of theairflow entering the fan nacelle 34 bypasses the core nacelle 12. Thebypass flow B within the bypass flow path 39 exits the fan nacelle 34through a nozzle exit area 40.

For the engine 10 shown in FIG. 1, a significant amount of thrust may beprovided by the bypass flow B due to the high bypass ratio. Thrust is afunction of density, velocity and area. One or more of these parameterscan be manipulated to vary the amount and direction of thrust providedby the bypass flow B. In one example, the engine 10 includes a structureassociated with the nozzle exit area 40 to change the physical area andgeometry to manipulate the thrust provided by the bypass flow B.However, it should be understood that the nozzle exit area might beeffectively altered by other than structural changes, for example, byaltering the boundary layer, which changes the flow velocity.Furthermore, it should be understood that any device used to effectivelychange the nozzle exit area is not limited to physical locations nearthe exit of the fan nacelle 34, but rather, includes altering the bypassflow B at any suitable location in the bypass flow path.

The engine 10 has a flow control device 41, indicated in FIG. 2 that isused to effectively change the nozzle exit area. In one example, theflow control device 41 provides the fan nozzle exit area 40 fordischarging axially the bypass flow B pressurized by the upstreamturbofan 20 of the engine 10. A significant amount of thrust is providedby the bypass flow B due to the high bypass ratio. The turbofan 20 ofthe engine 10 is designed for a particular flight condition, typicallycruise at 0.8 Mach and 35,000 feet. The turbofan 20 is designed at aparticular fixed stagger angle for an efficient cruise condition. Theflow control device 41 is operated to vary the nozzle exit area 40 toadjust fan bypass airflow such that the angle of attack or incidence onthe fan blade is maintained close to design incidence at other flightconditions, such as landing and takeoff. This enables desired engineoperation over a range of flight conditions with respect to engineperformance and other engine operational parameters such as noise level.In one example, the flow control device 41 defines a nominal convergedposition for the nozzle exit area 40 at cruise and climb conditions, andradially opens relative thereto to define a diverged nozzle position forother flight conditions. The flow control device 41 provides anapproximately 20% change in the nozzle exit area 40.

In one example, the flow control device 41 includes multiple hingedflaps 42 arranged circumferentially about the rear of the fan nacelle34. The hinged flaps 42 can be actuated independently and/or in groupsusing segments 44. In one example, the segments 44 and each hinged flap42 can be moved angularly using actuators 46. The segments 44 are guidedby tracks 48 in one example.

A controller 50 is programmed to command the flow control device 41 toeffectively change the nozzle exit area 40 for achieving a desiredengine operating condition. In one example, sensors 52-60 communicatewith the controller 50 to provide information indicative of an undesiredengine operating condition. In the example shown in FIG. 2, thecontroller 50 commands actuators 46 to move the flaps to physicallyincrease or decrease the size of the nozzle exit area 40.

In the examples shown, the engine 10 is a high bypass turbofanarrangement. In one example, the bypass ratio is greater than 10:1, andthe turbofan diameter is substantially larger than the diameter of thelow pressure compressor 16. The low pressure turbine 18 has a pressureratio that is greater than 5:1, in one example.

The gear train 22 is an epicyclical gear train, for example, which isshown in FIG. 3. In one example, the epicyclical gear train is a stargear train, providing a gear reduction ratio of greater than 2.5:1. Thegear train 22 includes a sun gear 70 that is coupled to the low spool14. Star gears 72 surround and mesh with the sun gear 70. The star gears72 are fixed against rotation about the sun gear 70 by rotationallysupporting the star gear 72 with structure grounded to the core nacelle12. A ring gear 74 surrounds and meshes with the star gears 72. Theturbofan 20 is driven by and connected to the ring gear 76. Thus, geartrain 22 rotationally drives the turbofan 20 at a slower speed relativeto low spool 14. As a result, a lower pressure ratio across the turbofan20 can be attained, which provides greater fuel efficiency. Further, theslower speed of the turbofan 20 as compared to the low spool 14 requiresless structural reinforcement than direct drive turbofan engines due tothe lower fan blade tip speed. Moreover, additional compressor andturbine stages can be eliminated since the low spool 14 can rotatefaster than the turbofan 20.

It should be understood, however, that the above parameters are onlyexemplary of a contemplated geared turbofan engine. Although an exampleembodiment of this invention has been disclosed, a worker of ordinaryskill in this art would recognize that certain modifications would comewithin the scope of this invention. For that reason, the followingclaims should be studied to determine the true scope and content of thisinvention.

1.-18. (canceled)
 19. A turbofan engine comprising: a fan nacellesurrounding a core nacelle that houses a spool, wherein the spool is alow spool, the core nacelle houses a high spool rotatable relative tothe low spool, and a low pressure compressor and turbine are mounted onthe low spool, the fan and core nacelles providing a bypass flow pathhaving a nozzle exit area; a turbofan arranged within the fan nacelleupstream from the core nacelle; a flow control device adapted toeffectively change the nozzle exit area to obtain a desired operatingcondition for the turbofan engine; and a gear train coupling the spooland turbofan for reducing a turbofan rotational speed relative to aspool rotational speed.
 20. The turbofan engine according to claim 19,wherein the flow control device includes a controller programmed toeffectively change the nozzle exit area in response to a conditiondetected by at least one sensor indicative of an undesired operatingcondition to obtain the desired operating condition.
 21. The turbofanengine according to claim 20, wherein the controller commands anactuator to physically change a size of the nozzle exit area.
 22. Theturbofan engine according to claim 19, wherein the gear train is anepicyclical gear train.
 23. The turbofan engine according to claim 22,wherein the epicyclical gear train is a star gear train.
 24. Theturbofan engine according to claim 19, wherein a high pressurecompressor and turbine are mounted on the high spool.
 25. A turbofanengine comprising: a fan nacelle surrounding a core nacelle that housesa spool, wherein the spool is a low spool, the core nacelle houses ahigh spool rotatable relative to the low spool, and a low pressurecompressor and turbine are mounted on the low spool, the fan and corenacelles providing a bypass flow path having a nozzle exit area; aturbofan arranged within the fan nacelle upstream from the core nacelle;a flow control device adapted to effectively change the nozzle exit areato obtain a desired operating condition for the turbofan engine; and anepicyclical gear train coupling the spool and turbofan for reducing aturbofan rotational speed relative to a spool rotational speed.
 26. Theturbofan engine according to claim 25, wherein the flow control deviceincludes a controller programmed to effectively change the nozzle exitarea in response to a condition detected by at least one sensorindicative of an undesired operating condition to obtain the desiredoperating condition.
 27. The turbofan engine according to claim 26,wherein the controller commands an actuator to physically change a sizeof the nozzle exit area.
 28. The turbofan engine according to claim 25,wherein the epicyclical gear train is a star gear train.
 29. Theturbofan engine according to claim 28, wherein the star gear trainprovides a gear reduction ratio of greater than 2.5:1.
 30. The turbofanengine according to claim 25, wherein the epicyclic gear train providesa gear reduction ratio of greater than 2.5:1.
 31. The turbofan engineaccording to claim 30, wherein the bypass flow path provides a bypassratio greater than 10:1.